Advances in on-site renewable energy technology have brought the concept of zero-energy buildings within reach.1 Many single-story residential and commercial buildings have enough favorably oriented roof area to make achieving zero energy techni­cally feasible, assuming no major solar obstructions exist and that energy efficiency has been aggressively implemented in the building design. As the number of stories increases, the potential to have a zero-energy building within the building’s footprint decreases. As efficiencies of photovoltaic (PV) cells increase, the potential to have zero-energy buildings increases.